stitcher function

.vscode/launch.json

···
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+    
+        {
+            "type": "node",
+            "request": "launch",
+            "name": "Launch Program",
+            "skipFiles": [
+                "<node_internals>/**"
+            ],
+            "program": "${workspaceFolder}/src/index.ts",
+            "preLaunchTask": "tsc: build - tsconfig.json",
+            "outFiles": [
+                "${workspaceFolder}/distribution/**/*.js"
+            ]
+        }
+    ]
+}

src/index.ts

···
 import fsp from 'fs/promises';
 import json5 from 'json5';
 import Sequencer from './sequencer.js';
+import { Stitcher } from './stitcher.js';
 import type {Programs, Segments, Sequences} from './sequencer.js';
 import type { Voices } from './voice.js';
 import type { Options } from 'openweather-api-node';
···
 const config: Config = json5.parse(await fsp.readFile(process.env['CONFIG'] || path.join('config', 'config.json5'), { encoding: 'utf-8' }));
 const sequence = await Sequencer(config);
 console.log(sequence.join('\n'));
-
+await Stitcher(sequence);
 
 export type { Config };

src/stitcher.ts

···
+import { spawn } from 'child_process';
+
+const ENCTOOL = process.env['ENCTOOL'] || 'ffmpeg';
+
+function ffmpeg(args: string[], files: number): Promise<void> {
+    return new Promise((resolve, reject) => {
+        console.log(`${ENCTOOL} ${args.join(' ')}`);
+        const process = spawn(ENCTOOL, args);
+        const to = setTimeout(async () => {
+            process.kill();
+            reject(new Error('timed out'));
+        }, 5000 * files);
+        process.on('exit', async (code) => {
+            clearTimeout(to);
+            if (code !== 0) {
+                reject(new Error(`exited with ${code}`));
+            }
+            else {
+                resolve();
+            }
+        });
+    });
+}
+
+async function Stitcher(files: string[]) {
+    const args: string[] = [];
+    files.forEach(f => args.push('-i', f));
+    args.push('-filter_complex', `[0:a][1:a][2:a]concat=n=${files.length}:v=0:a=1[out]`);
+    args.push('-map', '[out]', '-ar', '44100', '-ac', '2', '-c:a', 'pcm_s16le', 'output.wav');
+    await ffmpeg(args, files.length);
+}
+
+export default Stitcher;
+export { Stitcher };

test/sequencer.test.ts

···
-import { describe, expect, it, vi, beforeEach } from 'vitest';
+import { describe, expect, it, vi } from 'vitest';
 import { type CurrentWeather, type Options } from 'openweather-api-node';
 import { Sequencer } from '../src/sequencer.js';
 import type { Config } from '../src/index.js';

test/stitcher.test.ts

···
+import { Stitcher } from '../src/stitcher.js';
+import { describe, expect, it, vi, beforeEach } from 'vitest';
+import { EventEmitter } from 'events';
+import { spawn } from 'child_process';
+
+const mockChildProcess = new (class MockChildProcess
+    extends EventEmitter {
+    kill = vi.fn(() => {
+        return true;
+    });
+})();
+
+vi.mock('child_process', () => {
+    return {
+        spawn: vi.fn(() => mockChildProcess)
+    }
+});
+
+describe('stitcher', () => {
+
+    beforeEach(() => {
+        vi.clearAllMocks();
+    });
+
+    it('passes the correct arguments to ffmpeg', async () => {
+        const p = Stitcher(['1.flac', 'dir/2.flac']);
+        mockChildProcess.emit('exit', 0, null);
+        await p;
+        expect(spawn).toBeCalledWith('ffmpeg', [
+            "-i",
+            '1.flac',
+            '-i',
+            'dir/2.flac',
+            '-filter_complex',
+            '[0:a][1:a][2:a]concat=n=2:v=0:a=1[out]',
+            '-map',
+            '[out]',
+            '-ar',
+            '44100',
+            '-ac',
+            '2',
+            '-c:a',
+            'pcm_s16le',
+            'output.wav'
+        ]);
+    });
+
+    it('throws an error when ffmpeg fails', async () => {
+        const p = Stitcher(['sound.mp3']);
+        mockChildProcess.emit('exit', 1, null);
+        await expect(p).rejects.toThrow('exited with 1');
+        expect(spawn).toBeCalledWith('ffmpeg', [
+            "-i",
+            'sound.mp3',
+            '-filter_complex',
+            '[0:a][1:a][2:a]concat=n=1:v=0:a=1[out]',
+            '-map',
+            '[out]',
+            '-ar',
+            '44100',
+            '-ac',
+            '2',
+            '-c:a',
+            'pcm_s16le',
+            'output.wav'
+        ]);
+    });
+
+    it('throws an error when ffmpeg takes longer than expected', { timeout: 6000 }, async () => {
+        await expect(Stitcher(['in.wav'])).rejects.toThrow('timed out');
+        expect(spawn).toBeCalledWith('ffmpeg', [
+            "-i",
+            'in.wav',
+            '-filter_complex',
+            '[0:a][1:a][2:a]concat=n=1:v=0:a=1[out]',
+            '-map',
+            '[out]',
+            '-ar',
+            '44100',
+            '-ac',
+            '2',
+            '-c:a',
+            'pcm_s16le',
+            'output.wav'
+        ]);
+    });
+});